A/C keeps cycling on and off - help!
 

This has probably been going on for a while, but with the hot weather hitting in mid July, I've finally decided to look at charging my A/C unit. I went to Autozone, got the Quest refill with the guage and hooked it into my low side port with the Jeep running. That's when I noticed what was going on. Pressure will rise up into the red, then the compressor will cycle off and pressure will drop to almost zero. The unit kicks back on and pressure again quickly rises up into the red and the unit cycles off.

I haven't put any R134 into the system, just attached the hose and guage to get a reading. For a few years, I've noticed this cycling on and off when the defrost was on or a/c was going, but it never bothered me and I didn't look into it.

Any ideas on how to troubleshoot? I purchased the Jeep new back in 1998 and I use it as my kick around / hauling crap vehicle so I don't want to spend a ton of money on it. (I have a newer Jeep Grand Cherokee Rocky Mountain I drive daily). The 1998 Cherokee Sport has a 4 liter 4x4 automatic transmission with 158,000 miles. BTW, it still runs like a champ!

I had a similar problem on my old BMW, it'd kick on and run for a second then kick immediately off. The air never got cold. It turns out that the PO had tried to refill the unit and overfilled it, causing an overpressure condition that kept tripping the compressor off. Now, I'm not saying that's your issue, but it wouldn't hurt to have someone with the proper equipment look at it.

OK, well I searched around a little more on the internet and someone had posted the compressor will do this if it's not charged enough. So, I went ahead and dumped in my can of 134 and about 1/2 way thru the pressure started coming up and the compressor kept running. Guess I have a leak somewhere and there wasn't enough coolant / lube in the system to keep the system going.

compressor
 

same thing happened with me and i had to replace the compressor

The compressor kicking on an off can ALSO be a sign of an OVER charged system.

Also, freon will always find a way to escape, especially when not being used. You many have difficulty finding the "leak".

I am having this exact problem on my 1999 jeep grand cherokee. It will cycle up to about 65 pressure reading right at the red line then turn off and the pressure will drop all the way down and then it just repeats this process. So it appears i have enough pressure because it gets to nearly the red line and then drops off.

Please let me know what to do??? I need AC!!

I ended up dumping a can in and running the system. the compressor stopped cycling in and out and the pressure held around 40. the ac was noticeably cooler. I then bought another bottle and emptied it in as well. All in all I put in about 25 oz one 15 oz bottle and then most of a 12 oz bottle. pressure is at 45 the top of the filled range. everything seems to work so far. will keep an eye on it...

Take it to a reputable shop and have them evac the system and do a vacuum check on it. Then have them put leak detection dye in and recharge it to spec. After about a week or so of driving with the a/c on, take it back and have them check for traces of the dye, that'll tell you right where the leak is (if there is one). Unless it's the evap core, then there's some digging involved...